Lap Time Variation Predicts Task Error During Dual-Task Walking In Cognitively Healthy Women

Abstract

Variation in lap time (LTV) during a fast pace 400m walk test is a new metric thought to be an early indicator of cognitive decline in older adults. While LTV has been found to associate with executive function, no study has examined the potential for LTV to predict capacity of the brain to divide attention and meet the demand of walking and performing other tasks simultaneously. PURPOSE: The purpose of this study was to test the hypothesis that greater LTV would associate with larger dual-task cost during walking. METHODS: Fifty-two cognitively healthy (MoCA>25) women across a broad age range (30-80y) performed fast pace walking while balancing a tray (Dual1) or balancing a tray while vocalizing serial subtractions by 7’s (Dual2). Task error was quantified by degrees of tray tilt and subtraction error. On a separate day, women completed a fast pace 400m walk test (40m x 10 laps) with time to complete each lap recorded. LTV was defined as standard deviation of residuals estimated from the random effects linear model where each lap time was regressed on a person-specific random intercept and random slope associated with lap. Women were categorized into tertiles based on LTV. Comparisons were made between tertiles using ANCOVA after adjusting for age, years of education, and mean lap time. RESULTS: Gait speed (p=0.57) or the percent change in gait speed (p=0.34) were not significantly different between tertiles for the Dual1 condition, but tilt angle was larger in women with greater LTV (tertiles 1 vs. 3: 1.37±0.12 vs. 1.94±0.11 degrees; p=0.006). During the Dual2 condition, women with greater LTV had faster gait speed (p=0.02), lower percent change in gait speed (tertiles 1 vs. 3: 20.5±2.8 vs. 9.3±2.6%, p=0.02), similar subtraction error (p=0.58), but larger tilt angle (tertiles 1 vs. 3: 1.24±0.19 vs. 2.09±0.17 degrees, p=0.007). CONCLUSION: Lap time variation identified women that exhibited greater difficulty balancing an object while walking suggesting that LTV may be sensitive to deficits in the ability to share neural substrate for sensorimotor function. Supported by a Women’s Health Research Scholar Grant award from the Laura W. Bush Institute of Women’s Health and University Medical Center in Lubbock, TX.